Methods for forming improved self-assembled patterns of block copolymers

ABSTRACT

A method for forming self-assembled patterns on a substrate surface is provided. First, a block copolymer layer, which comprises a block copolymer having two or more immiscible polymeric block components, is applied onto a substrate that comprises a substrate surface with a trench therein. The trench specifically includes at least one narrow region flanked by two wide regions, and wherein the trench has a width variation of more than 50%. Annealing is subsequently carried out to effectuate phase separation between the two or more immiscible polymeric block components in the block copolymer layer, thereby forming periodic patterns that are defined by repeating structural units. Specifically, the periodic patterns at the narrow region of the trench are aligned in a predetermined direction and are essentially free of defects. Block copolymer films formed by the above-described method as well as semiconductor structures comprising such block copolymer films are also described.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.11/969,496, filed Jan. 4, 2008, which is a divisional of U.S. patentapplication Ser. No. 11/345,812, filed Feb. 2, 2006, now U.S. Pat. No.7,347,953, the entire content and disclosure of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention generally relates to the self-assembly of blockcopolymer materials into periodic patterns (i.e., patterns defined byrepeating structural units) on a particular surface. More particularly,the present invention provides a method that employs substratestructures of improved surface geometry for enhancing alignment of theself-assembled periodic patterns of a block copolymer along apredetermined direction as well as for reducing defects in theself-assembled periodic patterns. The present invention also relates toa semiconductor structure that comprises a block copolymer layer havingimproved periodic patterns, as well as to the block copolymer layeritself.

BACKGROUND OF THE INVENTION

Self-assembly of materials can be defined as the spontaneousorganization of materials into ordered patterns without the need forhuman interference. Examples of material self-assembly range fromsnowflakes to seashells to sand dunes, all of which form some type ofregular or ordered patterns in response to the external conditions.

Among various self-assembling materials, self-assembling blockcopolymers have attracted attention. Each self-assembling blockcopolymer typically contains two or more different polymeric blockcomponents that are immiscible with one another. Under suitableconditions, the two or more immiscible polymeric block componentsseparate into two or more different phases on a nanometer scale andthereby form ordered patterns of isolated nano-sized structural units.

Such ordered patterns of isolated nano-sized structural units formed bythe self-assembling block copolymers may potentially be used forfabricating periodic nano-scale structural units and therefore havepromising applications in semiconductor, optical, and magnetic devices.Specifically, dimensions of the structural units so formed are typicallyin the range of 10 nm, which are extremely difficult to define using theconventional lithographic techniques. Further, the block copolymers arecompatible with conventional semiconductor, optical, and magneticprocesses, and structural units formed by the block copolymers cantherefore be readily integrated into semiconductor, optical, andmagnetic devices.

Most potential applications of the self-assembled block copolymerpatterns require such patterns to be aligned in a predetermineddirection and to be essentially free of defects. There is therefore acontinuing need for improving the alignment of the self-assembledpatterns of block copolymers and for reducing defects in such patterns.

SUMMARY OF THE INVENTION

The present invention employs substrate structures of improved surfacegeometry for enhancing alignment of the self-assembled periodic patternsof a block copolymer along a predetermined direction as well as forreducing defects in the self-assembled periodic patterns.

In one aspect, the present invention relates to a method of formingperiodic patterns on a substrate surface, comprising:

applying a layer of a block copolymer that comprises two or moredifferent polymeric block components that are immiscible with oneanother over a substrate that comprises a substrate surface with atrench therein, wherein the trench includes at least one narrow regionflanked by two wide regions, and wherein the trench has a widthvariation of more than 50%; and

annealing the block copolymer layer to form periodic patterns inside thetrench, wherein the periodic pattern is defined by repeating structuralunits, and wherein the periodic patterns at the narrow region of thetrench are aligned in a predetermined direction and are essentially freeof defects.

Another aspect of the present invention relates to a semiconductorstructure, which comprises:

a substrate having a substrate surface with a trench therein, whereinthe trench includes at least one narrow region flanked by two wideregions, and wherein the trench has a width variation of more than 50%;and

a block copolymer layer located in the trench on a surface of asubstrate, wherein the block copolymer layer comprises periodic patternsdefined by repeating structural units, and wherein the periodic patternsat the narrow region of the trench are aligned in a predetermineddirection and are essentially free of defects.

A further aspect of the present invention relates to a block copolymerlayer having periodic patterns defined by repeating structural units,wherein the block copolymer layer includes at least one narrow regionflanked by two wide regions with a width variation of more than 50%therebetween, and wherein the periodic patterns at the narrow region arealigned in a predetermined direction and are essentially free ofdefects.

Other aspects, features and advantages of the invention will be morefully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a pattern that is formed by a block copolymer withpolymeric block components A and B, while the pattern comprises anordered array of spheres composed of the polymeric block component B ina matrix composed of the polymeric block component A.

FIG. 2 shows a pattern that is formed by a block copolymer withpolymeric block components A and B, while the pattern comprises anordered array of cylinders composed of the polymeric block component Bin a matrix composed of the polymeric block component A.

FIG. 3 shows a pattern that is formed by a block copolymer withpolymeric block components A and B, while the pattern comprisesalternating lamellae composed of the polymeric block components A and B.

FIG. 4 shows a pattern that is formed by a block copolymer withpolymeric block components A and B, while the pattern comprises anordered array of cylinders composed of the polymeric block component Ain a matrix composed of the polymeric block component B.

FIG. 5 shows a pattern that is formed by a block copolymer withpolymeric block components A and B, while the pattern comprises anordered array of spheres composed of the polymeric block component A ina matrix composed of the polymeric block component B.

FIG. 6 is a top-down scanning electron microscopic (SEM) photograph of ablock copolymer thin film, where the thin film contains periodicpatterns defined by randomly oriented alternating lamellae withsubstantial defects.

FIG. 7A shows a top-view of an exemplary substrate that contains atrench with more than 50% width variation, according to one embodimentof the present invention.

FIG. 7B shows a cross-sectional view of the substrate in FIG. 7A alongthe I-I line.

FIGS. 8-10 show top-views of several exemplary substrates that eachcontains a trench with more than 50% width variation, according tospecific embodiments of the present invention.

FIG. 11 shows a cross-sectional view of a substrate having a trench withvertically arranged alternating lamellae structures therein, accordingto one embodiment of the present invention.

FIG. 12 shows a cross-sectional view of a substrate having a trench withan array of horizontally aligned cylindrical structures therein,according to one embodiment of the present invention.

FIGS. 13-15 show top-down SEM photographs of block copolymer thin filmsformed in trenches on substrate surfaces, where the trenches each hasmore than 50% width variation, and the block copolymer thin films eachcomprises periodic patterns defined by alternating lamellae structuresthat are vertically arranged in the trenches, according to specificembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

In the following description, numerous specific details are set forth,such as particular structures, components, materials, dimensions,processing steps and techniques, in order to provide a thoroughunderstanding of the present invention. However, it will be appreciatedby one of ordinary skill in the art that the invention may be practicedwithout these specific details. In other instances, well-knownstructures or processing steps have not been described in detail inorder to avoid obscuring the invention.

It will be understood that when an element as a layer, region orsubstrate is referred to as being “on” or “over” another element, it canbe directly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” or “directly over” another element, there are no interveningelements present. It will also be understood that when an element isreferred to as being “connected” or “coupled” to another element, it canbe directly connected or coupled to the other element or interveningelements may be present. In contrast, when an element is referred to asbeing “directly connected” or “directly coupled” to another element,there are no intervening elements present.

The term “width variation” as used herein refers to the variation ofwidth in different regions of a structure, which is calculated as(W_(L)−W_(S))/W_(L), wherein W_(L) is the width measured at the widestregion of the structure, and wherein W_(S) is the width measured at thenarrowest region of the structure.

The term “annealing” or “anneal” as used herein refers to treatment ofthe block copolymer so as to allow sufficient phase separation betweenthe two or more different polymeric block components of the blockcopolymer in forming an ordered pattern defined by repeating structuralunits. Annealing of the block copolymer in the present invention can beachieved by various methods known in the art, including, but not limitedto: thermal annealing (either in a vacuum or in an inert atmospherecontaining nitrogen or argon), solvent vapor-assisted annealing (eitherat or above room temperature), or supercritical fluid-assistedannealing. As a specific example, thermal annealing of the blockcopolymer can be conducted at an elevated temperature that is above theglass transistor temperature (T_(g)) but below the degradationtemperature (T_(d)) of the block copolymer, as described in greaterdetail hereinafter. Other well-known annealing methods will not be beendescribed in detail in order to avoid obscuring the invention.

The term “defect” or “defects” as used herein refers to any perturbationin the translational or orientational order of a pattern. For example,when the pattern is defined by alternating lamellae, all the lamellae insuch a pattern must be aligned along the same direction in order for thepattern to be considered defect-free. Defects in the lamellar patternscan have various forms, including dislocation (i.e., line defectsarising from perturbations in the translational order), disclination(i.e., line defects arising from perturbations in the orientationalorder), spiral-shaped defects, or target-shaped defects.

The term “essentially free of defects” as used herein defines a defectdensity of less than about 1 defect per μm².

The present invention employs substrate structures of improved surfacegeometry to enhance alignment of the self-assembled periodic patterns ofblock copolymers along predetermined directions. Specifically, thesubstrate structures of the present invention each comprises on itssurface a trench of significant width variation, i.e., the trenchcomprises at least one relatively narrow region that is flanked by tworelatively wide regions, and the width of the trench at the narrowregion is significantly smaller than the width at the wide regions.Preferably, but not necessarily, the width variation between the narrowregion of the trench and the wide regions of the trench is more than50%, i.e., the width at the wide regions of the trench is more thantwice larger than that at the narrow region.

It has been discovered by the inventors of the present invention thatsuch an improved substrate with a trench of significant width variationfunctions to facilitate alignment of the self-assembled periodicpatterns of block copolymers at the narrow region of the trench. Theself-assembled periodic patterns of block copolymers align almostperfectly along the longitudinal axis of the trench at the narrow regionof the trench.

Further, the wide regions that flank the narrow region of the trenchfunction as “defect sinks” that facilitate diffusion of defects awayfrom the narrow region as well as annihilation of the defects.Consequently, the presence of a defect in the narrow region of thetrench becomes energetically less favorable, and therefore theself-assembled periodic patterns of block copolymers formed at thenarrow region of the trench are essentially free of defects.

There are many different types of block copolymers that can be used forforming the self-assembled periodic patterns. As long as a blockcopolymer contains two or more different polymeric block components thatare not immiscible with one another, such two or more differentpolymeric block components are capable of separating into two or moredifferent phases on a nanometer scale and thereby form patterns ofisolated nano-sized structural units under suitable conditions.

In a preferred, but not necessary, embodiment of the present invention,the block copolymer consists essentially of a first polymeric blockcomponent A and a second polymeric block component B that are immisciblewith each other. More preferably, one of the components A and B isselectively removable without having to remove the other, so as to formeither isolated and orderly arranged structural units composed of theun-removed component, or a continuous structural layer containingisolated and orderly arranged cavities formed after the removablecomponent has been removed. Alternatively, the components A and B maysimply have different electrical, optical, and/or magnetic properties,so that the ordered patterns composed of such components A and B can beused for fabricating different device structures.

The block copolymer used in the present invention may contain anynumbers of the polymeric block components A and B arranged in anymanner. The block copolymer can have a linear or branched structure.Preferably, such a block polymer is a linear diblock copolymer havingthe formula of A-B. Further, the block copolymer can have any one of thefollowing formula:

Specific examples of suitable block copolymers that can be used forforming the self-assembled periodic patterns of the present inventionmay include, but are not limited to:polystyrene-block-polymethylmethacrylate (PS-b-PMMA),polyethyleneoxide-block-polyisoprene (PEO-b-PI),polyethyleneoxide-block-polybutadiene (PEO-b-PBD),polyethyleneoxide-block-polystyrene (PEO-b-PS),polyethyleneoxide-block-polymethylmethacrylate (PEO-b-PMMA),polyethyleneoxide-block-polyethylethylene (PEO-b-PEE),polystyrene-block-polyvinylpyridine (PS-b-PVP),polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-polyferrocenyldimethylsilane (PS-b-PFS),polybutadiene-block-polyvinylpyridine (PBD-b-PVP), andpolyisoprene-block-polymethylmethacrylate (PI-b-PMMA).

The specific self-assembled periodic patterns formed by the blockcopolymer are readily determined by the molecular weight ratio betweenthe first and second polymeric block components A and B.

Specifically, when the ratio of the molecular weight of the firstpolymeric block component A over the molecular weight of the secondpolymeric block component B is greater than about 80:20, the blockcopolymer will form an ordered array of spheres composed of the secondpolymeric block component B in a matrix composed of the first polymericblock component A, as shown in FIG. 1.

When the ratio of the molecular weight of the first polymeric blockcomponent A over the molecular weight of the second polymeric blockcomponent B is less than about 80:20 but greater than about 60:40, theblock copolymer will form an ordered array of cylinders composed of thesecond polymeric block component B in a matrix composed of the firstpolymeric block component A, as shown in FIG. 2.

When the ratio of the molecular weight of the first polymeric blockcomponent A over the molecular weight of the second polymeric blockcomponent B is less than about 60:40 but is greater than about 40:60,the block copolymer will form alternating lamellae composed of the firstand second polymeric block components A and B, as shown in FIG. 3.

When the ratio of the molecular weight of the first polymeric blockcomponent A over the molecular weight of the second polymeric blockcomponent B is less than about 40:60 but greater than about 20:80, theblock copolymer will form an ordered array of cylinders composed of thefirst polymeric block component A in a matrix composed of the secondpolymeric block component B, as shown in FIG. 4.

When the ratio of the molecular weight of the first polymeric blockcomponent A over the molecular weight of the second polymeric blockcomponent B is less than about 20:80, the block copolymer will form anordered array of spheres composed of the first polymeric block componentA in a matrix composed of the second polymeric block component B, asshown in FIG. 5.

Therefore, the molecular weight ratio between the first and secondpolymeric block components A and B can be readily adjusted in the blockcopolymer of the present invention, in order to form desiredself-assembled periodic patterns.

In a particularly preferred embodiment of the present invention, theblock copolymer used for forming the self-assembled periodic patterns ofthe present invention is PS-b-PMMA. PS and the PMMA blocks in such aPS-b-PMMA block copolymer can each have a molecular weight ranging fromabout 10 kg/mol to about 100 kg/mol, with a molecular weight from about20 kg/mol to about 50 kg/mole being more typical.

The surface energies of PS and PMMA have been reported to be γ_(PS)=40.7dyn/cm and γ_(PMMA)=41.1 dyn/cm at 20° C. respectively. Water contactangles for polystyrene range around 84-91°, whereas for PMMA they arearound 75°.

Typically, mutual repulsion between different polymeric block componentsin a block copolymer is characterized by the term χN, where χ is theFlory-Huggins interaction parameter and N is the degree ofpolymerization. The higher χN, the higher the repulsion between thedifferent blocks in the block copolymer, and the more likely the phaseseparation therebetween. When χN>10 (which is hereinafter referred to asthe strong segregation limit), there is a strong tendency for the phaseseparation to occur between different blocks in the block copolymer.

For a PS-b-PMMA diblock copolymer, χ can be calculated as approximately0.028+3.9/T, where T is the absolute temperature. Therefore, χ isapproximately 0.0362 at 473K (≈200° C.). When the molecular weight(M_(n)) of the PS-b-PMMA diblock copolymer is approximately 51 Kg/mol,with a molecular weight ratio (PS:PMMA) of approximately 50:50, thedegree of polymerization N is about 499.7, so χN is approximately 18.1at 200° C. Alternatively, when M_(n) of the PS-b-PMMA diblock copolymeris approximately 64 Kg/mol, with a molecular weight ratio (PS:PMMA) ofapproximately 66:34, the degree of polymerization N is about 622.9, soχN is approximately 22.5 at 200° C.

Therefore, by adjusting one or more parameters such as the composition,the total molecular weight, and the annealing temperature, the mutualcompulsion between the different polymeric block components in the blockcopolymer of the present invention can be readily controlled toeffectuate desired phase separation between the different blockcomponents. The phase separation in turn leads to formation ofself-assembled periodic patterns, which comprise repeating structuralunits (i.e., spheres, cylinders, or lamellae) composed of differentblock components, as described hereinabove.

The periodicity or the dimension (L₀) of the repeating structural unitsin the periodic pattern is determined by intrinsic polymeric propertiessuch as the degree of polymerization N and the Flory-Huggins interactionparameter χ. At the strong segregation limit, L₀˜N^(2/3)χ^(1/6). Inother words, L₀ scales with the degree of polymerization N, which inturn correlates with the molecular weight M_(n) and the molecular weightratio between different polymeric block components. Therefore, byadjusting the composition and the total molecular weight of the blockcopolymer of the present invention, the dimensions of the repeatingstructural units can be readily tuned.

In order to form the self-assembled periodic patterns, the blockcopolymer is first dissolved in a suitable solvent system to form ablock copolymer solution, which is then applied onto the substratesurface to form a thin block-copolymer layer, followed by annealing ofthe thin block-copolymer layer, thereby effectuating phase separationbetween different polymeric block components contained in the blockcopolymer.

The solvent system used for dissolving the block copolymer and formingthe block copolymer solution may comprise any suitable solvent,including, but not limited to: toluene, propylene glycol monomethylether acetate (PGMEA), propylene glycol monomethyl ether (PGME), andacetone. The block copolymer solution preferably contains the blockcopolymer at a concentration ranging from about 0.1% to about 2% bytotal weight of the solution. More preferably, the block copolymersolution contains the block copolymer at a concentration ranging fromabout 0.5 wt % to about 1.5 wt %. In a particularly preferred embodimentof the present invention, the block copolymer solution comprises about0.5 wt % to about 1.5 wt % PS-b-PMMA dissolved in toluene or PGMEA.

The block copolymer solution can be applied to the substrate surface byany suitable techniques, including, but not limited to: spin casting,coating, spraying, ink coating, dip coating, etc. Preferably, the blockcopolymer solution is spin cast onto the substrate surface to form athin block copolymer layer.

After application of the thin block copolymer layer onto the substratesurface, the entire substrate is annealed to effectuate micro-phasesegregation of the different block components contained by the blockcopolymer, thereby forming the periodic patterns with repeatingstructural units.

As mentioned hereinabove, annealing of the block copolymer in thepresent invention can be achieved by various methods known in the art,including, but not limited to: thermal annealing (either in a vacuum orin an inert atmosphere containing nitrogen or argon), solventvapor-assisted annealing (either at or above room temperature), andsupercritical fluid-assisted annealing, which are not described indetail here in order to avoid obscuring the invention.

In a particularly preferred embodiment of the present invention, athermal annealing step is carried out to anneal the block copolymerlayer at an elevated annealing temperature that is above the glasstransition temperature (T_(g)) of the block copolymer but below thedecomposition or degradation temperature (T_(d)) of the block copolymer.More preferably, the thermal annealing step is carried out an annealingtemperature of about 200° C.-300° C. The thermal annealing may last fromless than about 1 hour to about 100 hours, and more typically from about1 hour to about 15 hours.

FIG. 6 shows a top-down scanning electron microscopic (SEM) photographof a block copolymer thin film, which is formed over a substantiallyplanar substrate surface. The thin film contains periodic patternsdefined by randomly oriented alternating lamellae composed of the firstand second polymeric block components A and B. The thickness of each Aor B lamellae (i.e., 0.5 L₀) is approximately 15 nm. The thin filmcontains a substantial number of randomly appearing or disappearinglamellae 2, which are undesirable defects.

As mentioned hereinabove, most applications of the self-assembly blockcopolymer films require the periodic patterns to be aligned in apredetermined direction, with little or no defects. In order to achievebetter alignment of the periodic patterns and reduce the defectscontained therein, the present invention provides improved substratestructures with novel surface geometry, i.e., surface trenches withsignificant width variation, in which the improved periodic patterns canbe formed.

FIG. 7A shows a top-view of an exemplary substrate 10 that contains asurface trench 12, according to one embodiment of the present invention.The surface trench 12 can be either closed ended (as shown in FIG. 7A)or open-ended (not shown), as long as such trench 12 contains at leastone relatively narrow region 12A that is flanked by two relatively wideregions 12B.

The width of the trench 12 at the narrow region 12A is referred toherein as W_(S), and the width of the trench 12 at the wide regions 12Bis referred to herein as W_(L). It is preferred that the width variationof the trench, which is calculated as (W_(L)−W_(S))/W_(L), is more than50% width variation. In other words, W_(L) is more than twice largerthan W_(S).

Such a surface trench 12 with more than 50% width variation isparticularly efficient in facilitating the alignment of the periodicpatterns during self-assembling of a block copolymer film (not shown).Specifically, the periodic patterns of the block copolymer film (notshown) formed in such a surface trench 12 align almost perfectly alongthe longitudinal axis of the trench at the narrow region 12A. Further,the wide regions 12B of the trench 12 function as “defect sinks” tofacilitate diffusion of defects away from the narrow region 12A as wellas annihilation of the defects. Consequently, the presence of a defectin the narrow region 12A of the trench 12 becomes energetically lessfavorable, and therefore the self-assembled periodic patterns of theblock copolymer film (not shown) are essentially free of defects at thenarrow region 12A of the trench 12.

FIG. 7B shows a cross-sectional view of the substrate 10 in FIG. 7Aalong the I-I line. It is preferred that the depth (h) of the trench 12is substantially uniform throughout the narrow region 12A and the wideregions 12B.

Various surface trench geometries can be used for practice of thepresent invention, as long as such trenches have sufficient widthvariations. For example, FIG. 8 shows a top view of another surfacetrench 14 (which can be either close-ended or open-ended) of a slightlydifferent shape, while trench 14 also contains at least one relativelynarrow region 14A that is flanked by two relatively wide regions 14B,while the trench width (W_(S)) at the narrow region 14A is less thanhalf of trench width (W_(L)) at the wide region 14B. FIG. 9 shows a topview of yet another surface trench 16 (which can be either close-endedor open-ended) of another shape, while trench 16 likewise contains atleast one relatively narrow region 16A that is flanked by two relativelywide regions 16B, where the trench width (W_(S)) at the narrow region16A is less than half of trench width (W_(L)) at the wide region 16B.FIG. 10 shows a top view of still another surface trench 18 (which canbe either close-ended or open-ended) of a further different shape, whiletrench 18 also contains at least one relatively narrow region 18A thatis flanked by two relatively wide regions 18B, while the trench width(W_(S)) at the narrow region 1 SA is less than half of trench width(W_(L)) at the wide region 18B.

Preferably, but not necessarily, the trench width (W_(S)) at the narrowregion of the above-described surface trenches ranges from about 1.5 L₀to about 20.5 L₀, more preferably from about 1.5 L₀ to about 10.5 L₀.The trench depth (h) preferably ranges from about 0.25 L₀ to about 3 L₀,and more preferably from about 0.5 L₀ to about 1 L₀. Note that typicalperiodicity of the block copolymer repeating structural units rangesfrom about 5 nm to about 100 nm, and more typically from about 10 nm toabout 50 nm. Still more typically, the periodicity ranges from about 15nm to about 50 nm.

As a specific example of the present invention, a lamellae-formingPS-b-PMMA block copolymer having a molecular weight of about 51 kg/moleis used for forming the self-assembled periodic patterns. Since L₀ isapproximately 30 nm for such a lamellae-forming PS-b-PMMA blockcopolymer, the preferred trench width (W_(S)) at the narrow region ofthe trench ranges from about 45 nm to about 615 nm, and more preferablyfrom about 45 nm to about 315 nm, while the preferred trench depth (h)ranges from about 7.5 nm to about 90 nm, and more preferably from about15 nm to about 30 nm.

In order to form the self-assembled periodic patterns, the thickness ofthe applied block copolymer layer needs to reach a critical value L₀. Ifthe block copolymer layer is thinner than L₀, the repeating structuralunits cannot be formed. On the other hand, if such a block copolymerlayer has a thickness that is a multiplicity of L₀, then multiple layersof repeating structural units will be formed.

In a particularly preferred embodiment of the present invention, it ispreferred to form a block copolymer film with a portion inside thetrench and a portion outside the trench, while the portion inside thetrench has a sufficient thickness (L₀) for self-assembling into a singlelayer of repeating structural units (i.e., similar to a monolayer)inside the trench, while the portion outside the trench does not havesufficient thickness for self-assembling and therefore remains amorphousor featureless, i.e., without any repeating structural units. In orderto achieve such a block copolymer film, the trench depth (h) preferablyranges from about 0.5 L₀ to about 1 L₀, so that application of a blockcopolymer layer of more than 0.5 L₀ thick but less than about 1 L₀ thickwill provide sufficient layer thickness in the trench forself-assembling of the block copolymer into a monolayer of repeatingstructural units, but not outside the trench. In other words, theoverall film thickness of the block copolymer layer is less than 1 L₀,so it is not sufficient to form self-assembled repeating structuralunits at most regions on the substrate surface. However, the surfacetrench collects extra block copolymer material to reach the criticalthickness of 1 L₀, thereby enabling self-assembling of the blockcopolymer material into repeating structural units inside the trench andonly inside the trench.

In order to maintain the defect-free characteristics of the periodicpatterns in the narrow region of the trench, it is preferred that thelength of the narrow region is not more than about 2 microns at a givenwidth (W_(S)) of about 1.5-2.5 L₀. When the trench width (W_(S)) at thenarrow region increase to about 2.5-4.5 L₀, the length of the narrowregion should not be more than about 0.6 micron, in order to reduce therisk of defect formation.

The surface trenches as described hereinabove can be readily formed byvarious well-known techniques. For example, conventional lithography andetching processes can be used to form a surface trench that has thedesired geometry and a trench depth ranging from about 5 nm to about 100nm, more typically of about 15-30 nm.

Upon application of the thin block copolymer layer over the substratesurface, followed by the annealing step, as described hereinabove, theblock copolymer self-assembles into periodic patterns that areself-aligned to the longitudinal axis of the surface trench at thenarrow region, with little or no defects thereat.

The present invention is applicable to both symmetric (i.e., havingsubstantially the same amount of blocks A and B) and non-symmetric(i.e., having significantly different amounts of blocks A and B) blockcopolymers. However, since the symmetric and non-symmetric blockcopolymers tend to form different periodic patterns (i.e., symmetricblock copolymers form alternating lamellae, while non-symmetric blockcopolymers form order arrays of either spheres or cylinders), the trenchsurface of the present invention has to be prepared differently in orderto form the desired wetting properties for aligning different periodicpatterns.

The wetting properties as discussed herein refer to the surfaceaffinities of a specific surface with respect to the different blockcomponents of the block copolymers. For example, if a surface hassubstantially the same surface affinity to both block components A and Bof a block copolymer, such a surface is considered a neutral surface ora non-preferential surface, i.e., both block components A and B can wetor have affinities to such a surface. In contrast, if a surface hassignificantly different surface affinities for the block components Aand B, such a surface is then considered a preferential surface, i.e.,only one of block components A and B can wet such a surface, but theother cannot.

Surfaces comprising one of silicon native oxides, silicon oxides, andsilicon nitrides are preferentially wetted by PMMA block components, butnot by PS block components. Therefore, such surfaces can be used aspreferential surfaces for PS-b-PMMA block copolymers. On the other hand,a monolayer comprising a substantially homogenous mixture of PS and PMMAcomponents, such as a random PS-r-PMMA copolymer layer, provides aneutral surface or a non-preferential surface for PS-b-PMMA blockcopolymers.

For lamellae-forming symmetric block copolymers, it is desired toarrange the alternating lamellae so formed in perpendicular to a bottomsurface of the trench. Therefore, it is desirable to provide a trenchwith a neutral or non-preferential bottom surface but preferentialsidewall surfaces.

FIG. 11 shows a cross-sectional view of a substrate 20 having a surfacetrench 22 defined by a bottom surface and sidewall surfaces. The bottomsurface is preferably coated with a neutral or non-preferential material24 and therefore forms a neutral or non-preferential surface, while thesidewall surfaces are preferably coated with a preferential material 26and therefore form preferential surfaces. The preferential material 26for example has preferential affinity for one of, but not the other of,the block components A and B contained in the block copolymer.

In this manner, a block copolymer film containing alternating lamellaestructures 32 and 34 formed of block components A and B can be formed insuch a surface trench 22. The bottom surface of the trench is wettableby both components A and B, while the sidewall surfaces are onlywettable by one of, but not the other of, block components A and B.Therefore, the alternating lamellae structures 32 and 34 are verticallyarranged, i.e., perpendicular to the bottom surface of the trench 22.

For cylinder-forming non-symmetric block copolymers, it is desired toarrange the cylinder arrays either parallel with, or perpendicular to,the bottom surface of the trench. For forming parallelly arrangedcylinder arrays, it is desirable to provide a trench with a preferentialbottom surface as well as preferential sidewall surfaces. In contrast,for forming perpendicularly arranged cylinder arrays, it is desirable toprovide a trench with a neutral or non-preferential bottom surface butpreferential sidewall surfaces.

FIG. 12 shows a cross-sectional view of a substrate 20 having a surfacetrench 22 defined by a bottom surface and sidewall surfaces, which arecoated with a preferential material 26 and therefore form preferentialsurfaces that have surface affinity for one of, but not the other of,block components A and B of the block copolymer. In this manner, a blockcopolymer film containing a single layer of ordered cylinders 32 (formedof one of block components A and B) in a matrix 34 (formed of the otherof block components A and B) can be formed in such a surface trench. Thebottom and sidewall surfaces of the trench 22 are only wettable to oneof, but not the other of, block components A and B. Therefore, thecylinders 32 are arranged horizontally, i.e., parallel to the bottomsurface of the trench.

For sphere-forming non-symmetric block copolymers, the trench shouldhave a preferential bottom surface as well as preferential sidewallsurfaces.

As a specific example of the present invention, a block copolymersolution, which contained 0.5 wt % lamellae-forming symmetric PS-b-PMMAwith a molecular weight of about 51 kg/mol in toluene, was spin cast at2000-5000 revolutions per minute (rpm) onto various substratescontaining surface trenches of different geometries. Each of the surfacetrenches had a width variation larger than 50%, and a trench depth ofabout 20 nm. The substrates were then annealed at about 250° C.-260° C.for about 10-12 hours, and the block copolymer films so formed are shownin FIGS. 13-15.

Specifically, FIGS. 13-15 are the SEM photographs of the resulting blockcopolymer films, each of which comprises alternating lamellae structuresthat are arranged perpendicular to the substrate surface. Note that thelamellae structures at the narrow regions of the trenches are almostperfectly aligned along the longitudinal axes of the trenches with nodefects.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A block copolymer layer comprising periodic patterns defined byrepeating structural units, wherein the block copolymer layer includesat least one narrow region flanked by two wide regions with a widthvariation of more than 50% therebetween, and wherein the periodicpatterns at the narrow region are aligned in a predetermined directionand are essentially free of defects.
 2. The block copolymer layer ofclaim 1, wherein the width of the at least one narrow region of thetrench ranges from about 1.5 L₀ to about 2.5 L₀, wherein to is theperiodicity of the repeating structural units in the periodic patterns,and wherein the narrow region has a length of not more than about 2microns.